Magnetic bubble memory devices are formed in epitaxial layers grown on gadolinium gallium garnet substrates. Such substrates are prepared from elongated monocrystals grown according to the well known Czochralski technique by pulling a seed rod from a melt. The melt is contained in an expensive iridium crucible, which is quite small and yet must contain sufficient melt to grow a monocrystal of a practical size. The problem is that the components of material for charging the crucible are primarily powders of Gd.sub.2 O.sub.3 and Ga.sub.2 O.sub.3 having a high ratio of voids to solids in their natural state. Consequently, it is essential to compact the materials to fit the small crucible so that sufficient melt is produced in a single step charging procedure followed by meltdown.
Conventionally, a proper mixture of powder was funnelled into elongated rubber pouches referred to as "bladders." The bladders were then sealed and placed in a pressure vessel filled with a slightly oily solution. The vessel was mechanically sealed and more solution was pumped into the vessel until the pressure therein rose to about 18,000 psi. The machine which includes the vessel and pump was referred to as an isostatic compactor because all surfaces of the bladder received application of the same amount of pressure. At least one body referred to as a "stick" of compacted powder was produced in the conventional procedure which stick measured from about 1.2 to about 1.5 inches in diameter and was about 8 inches long. Bundles of such sticks, were vertically disposed on top of broken sticks in an iridium crucible for meltdown. The problem was that the procedure was time consuming and the sticks were irregular in shape so they did not always melt down uniformly. Consequently, an unmelted part of a stick sometimes toppled out of the crucible causing damage to furnace equipment. It is preferable to prepare a singular, well defined body of compacted powder for each charge such that the posture of the body will be stable during meltdown.